Improvement of Hargreaves–Samani Reference Evapotranspiration Estimates in the Peruvian Altiplano

The FAO 56 Penman–Monteith equation (PM) is considered the most accurate method for estimating reference evapotranspiration (ETo). However, PM requires a large amount of data that not always available. Thus, objective this study to improve Hargreaves–Samani (HS) estimates in Peruvian Altiplano (PA) by calibrating radiation coefficient KRS. results show modified HS (HSM) ETo at validation after KRS calibration, revealing evident improvements accuracy with Nash–Sutcliffe efficiency (NSE) between 0.58 and 0.93, percentage bias (PBIAS) −0.58 1.34%, mean absolute error (MAE) −0.02 0.05 mm/d, root square (RMSE) 0.14 0.25 mm/d. Consequently, multiple linear regression (MLR) model was used regionalize PA. It concluded that, absence meteorological data, HSM can be new values instead